Photographic developer systems



United States Patent 3,512,972 PHOTOGRAPHIC DEVELOPER SYSTEMS Laura K.Case, Winchester, Mass., assignor to Itek Corporation, Lexington, Mass,a corporation of Delaware No Drawing. Filed Apr. 5, 1965, Ser. No.445,743

Int. Cl. G03c 5/24 U.S. Cl. 96-48 20 Claims ABSTRACT OF THE DISCLOSUREform a latent metal image in the exposed portions of the copy medium,and-then contacted with a developer comprising ascorbic acid and capricion. The preferred system contains an acid acceptor such as an amine.

The present invention relates to data storage systems and methods, andrelates in particular to systems and methods for image reproduction.

It is known from commonly owned copeding applications Ser. No. 199,211filed May 14, 1962, of E. Berman et al., now abandoned, and Ser. No.445,797 filed Apr 5, 1965 of Ronald Francis, now U.S. Patent No.3,445,230 that certain photo-sensitive materials, including pigmentssuch as titanium dioxide and metal carbonyls such as chromium, tungsten,and molybdenum carbonyls, can be rendered reactive with reducible metalions by exposure to activating radiation. The reaction of the exposedmaterial with metal ions causes formation of free metal, which isdeposited as a finely divided precipitate.

The phenomenon can be used for image reproduction. For example, when thelight-sensitive materials, incorporated in a copy medium, are exposed toan image pattern of radiation and then developed by contact of themedium with a reducible metal ion, a latent image comprising free metalis formed in the copy medium.

It is further known that latent metal images of this type can beamplified or intensified by bringing the latent images into contact withsilver ion and a redox system, usually an organic redox system, such ashydroquinone, metol, or phenidone, for example. When metal is alreadypresent in the latent image on the copy medium, additional metal isprecipitated by reaction of silver ion with the reducing components ofthe redox system. Analogous amplification or intensification systemshave heretofore been used in the art for the development of images insilver halide photography, for example. A disadvantage of this prior artimage intensification process is its dependence on the use of silver, amaterial which is bottoming increasingly more rare and more expensive.

According to the present invention, it has been discovered that imageintensification or amplification can be effected employing systems usingcupric ion as the redicible metal ion in the image intensifying step. Inparticular, cupric ion has been employed according to the presentinvention to amplify latent images comprising ice free metals,particularly images of copper and silver.

Compositions suitable for the non-electrolytic deposition of copper areknown in the prior art, for example mixtures of Rochelle salts, copperion, and formaldehyde. However, such compositions give a uniformdeposition of copper and if employed in an attempt to develop an imageaccording to the present invention, they deposit copper indiscriminatelyover both image areas and background areas, without preferentialdeposition.

The developing compositions of the present invention comprise cupric ionin combination with ascorbic acid and, suitably, an acid acceptor. It isknown in the prior art that ascorbic acid reduces cupric ion to copper,and the reaction has been used in analytic chemistry. However, theautocatalytic nature of the reaction, critically resulting in selectivedeposition of copper where metal is already present, has heretofore notbeen recognized in the art. This selective autocatalytic feature bringsabout the preferential deposition of copper metal in those areas of anexposed and developed data processing medium in which a latent image ofdeposited metal already exists, resulting in amplification of the latentimage without a corresponding intensification of the background.

Cupric ion and asconbic acid react with the formation ofdehydro-ascorbic acid and free copper according to the equation:

The equilibrium of this reaction can be displaced by the presence of anacid acceptor neutralizing hydrogen ions formed in the reaction.Accordingly, in the preferred compositions of the present invention, anacid acceptor is present.

As acid acceptors in the system of the invention, any basic material notprecipitating copper hydroxides can be employed. In general, inorganichydroxides are not suitable, but ammonium hydroxide can be employed,apparently because formation of copper ammonia complexes discourages theprecipitation of copper hydroxides. Amine acceptor materials are,however, the preferred reagents. Amines of the widest variety can beemployed, including primary, secondary, and tertiary aliphatic,cycloaliphatic, and aromatic amines, including isocyclic andheterocyclic compounds. The amines need not be hydrocarbon materials,but include such substituted amines as triethanol amine, and urea.Cycloaliphatic amines such as N-methyl cyclohexyl amine can be employed,as can heterocyclic amines such as pyrrole, imidazole, quinoline,morpholine, and hexamethylenetetramine. Since the principal function ofthe amine or NH OH acid acceptor is to neutralize hydrogen ions, thechemical structure of the acid acceptor is immaterial providing only, asmentioned earlier, that the material is not one precipitating copperhydroxides. What is critical to the present invention is the well-knownproperty of amines to accept or neutralize hydrogen ions.

In the present specification and claims, the term nitrogenous acidacceptor is used to define amine materials of the type discribed andammonium hydroxide as the sole inorganic acid acceptor.

In general, in preparing the image intensifying composition of thepresent invention, ascorbic acid and cupric ion can be present in widelyvaried proportions. While it is preferred to have substantiallyequimolar quantities of the materials present in view of the reactionbetween the substances, images will be formed if according to theinvention either of the components is in a ration of 100:1 to the other.Suitably, the components are present in a :1 or 1:10 ratio to avoidwaste. If an acid acceptor is present, substantially equimolarquantities of the acceptor and ascorbic acid are preferred, but the acidacceptor can be used in amounts as slight as mol percent of the acidemployed. Large amounts of acid acceptor tend to cause precipitation ofcopper hydroxides, and are preferably avoided.

With these concentration ranges for the reagents in the amplifyingcompositions, the optical densities of amplified images producedaccording to the present invention will vary from about 0.1 to greatedthan 1, measured by diffuse reflectance.

In general, the time required for development of a latent image byamplification is between about seconds and about 5 minutes when an acidacceptor is present in the solutions. If no acceptor is present in thesolutions, the time of development may vary from between about 2 minutesto about minutes. Still longer development times can be employed, butthere is in general no observable improvement in the image after theperiod of time indicated.

As mentioned earlier, the copper-containing amplifying compositions andthe techniques of the present invention can be used to amplify latentmetal images, particularly ion and exposed to light, whereupon a latentimage of copper metal is formed in the light struck areas. The copymedium, still having residual cupric ion thereon, is then suitablysimply contacted with a mixture of ascorbic acid and an acid acceptor,additional copper metal is deposited in the image areas where the latentimage of copper metal already exists, and the latent image is madevisible.

A better understanding of the present invention and of its manyadvantages will be had by referring to the following. specific examplesgiven by way of illustration.

EXAMPLES 1-17 For each of Examples 1-17, a primary silver image wasprepared as follows. Titanium dioxide dispersed in a commercial acrylateresin binder (Rhoplex) commonly employed in the photosensitive-papercoating art was used to coat paper stock to form a copy medium. Afterdrying, the coated paper was exposed to an image pattern of radiationfrom a 6 watt black light Raymaster fluorescent bulb for seconds. Theirradiated sample was then immersed in a saturated solution ofmethanolic silver nitrate for 10 seconds, washed in a 50:50 mixture ofmethanol and water for one minute, fixed in a sodium thiosulfate fixerbuffered with sodium sulfite and sodium bisulfite for 15 minutes, washedin tap water for 30 minutes, and then dried.

TABLE I.-EXAMPLES 1-17 Ascorbic acid Cu(NOa)z D Image Characteristicsev. Vol. Cone. Vol. Cone. Vol. Cone. time, Visual Optical 13856 (m1.)sec. appearance density 10 1 l0 1 Triethanolamine (in OH OH) 10 0. 751.12 10 1 10 1 Urea 15 1 0.60 10 0. 1 10 1 Hexamethylenetetramine 10 0.1 0. 88 10 1 10 0.1 .d0 10 0.1 0.80 10 1 10 0. 1 Triethanolamine.-. 100. 1 0. 63 10 0.1 10 0. 1 -....d 10 0.1 0.86 10 0. 1 10 0. 1 NH 2 1. 50. 78 10 0.5 10 0.35 Imidazole (1n 0113011) 5 0.35 0.67 10 0. 5 10 0. 5Pyrrole (1n CHaOH) 10 0. 5 0.32 10 1 10 1 Quinolme (in ClIaOH) 10 0.5 0.62 10 0.6 10 0.5 Dodecylamlne (1n CHaOH) 3 0. 5 0.90 10 1 10 1 Aniline(1n CHaOH) 10 1 0.99 15 1 10 1 do 5 1 1.10 10 0.2 25 0. 1 1,1,3,3tetramethyl guanidine (in 10 0.2 0. 78

CHQOH). 10 0, 5 10 0.5 Morpholine 5 1 0. 62 15 0. 35 15 0. 35N-methylcyclohexylamine (in 2 1 0. 62

CHaOH). 10 0 1 10 0. 01 Hexamethylene tetramine 10 0.1 0.25

those of silver or copper. The latter metals are of principal commercialimportance in the photographic arts. However, the systems of the presentinvention can be used to amplify images comprising other metals,particularly of metals at least as noble as copper, such as images ofpalladium, platinum, gold, etc.

Latent silver images are formed, for example, by irradiation of a copymedium comprising a readiation sensitive substance such as titaniumdioxide or a metal carbonyl, as disclosed in the aforementioned US.patent applications, with subsequent contact of the exposed medium witha solution of silver ion. Metallic silver is deposited on the medium toform a latent image. Contact of the latent silver image with the copperion-ascorbic acid compositions of the present invention will causemetallic copper to be deposited on the medium in image areas Wheresilver is already present.

The copper ion-ascorbic acid compositions of the present invention canalso advantageously be employed to intensify latent images of copper. Oncontact of cupric ion with irradiated TiO for example, cuprous ion isformed. On heating, the cuprous ion disproportionates with formation ofmetallic copper. Latent images of metallic copper can also be formed ifcopper ion is present in contact with a photosensitive pigment such astitanium dioxide at the time of exposure to activating radiation. Theresultant latent copper images can then subsequently be amplified withthe compositions of the present invention.

For example, a copy medium having a titanium dioxide coating thereon canbe contacted with a solution of cupric The resultant primary latentsilver image was amplified by immersion of the copy medium into avariety of aqueous solutions containing copper ion, ascorbic acid, andan acid acceptor. These experiments are summarized in accompanying TableI.

Alternatively, free silver latent images can be formed by exposing acopy medium comprising tungsten carbonyl to an image pattern ofultraviolet light and then contacting the medium with a solution ofsilver ion, as in copending application (CMS 32527).

Contact of the exposed copy medium with solutions of ions of gold,palladium, platinum, etc., rather than silver ion, results in theformation of latent images comprising these free metals respectively.

EXAMPLE 18 A silver halide emulsion-coated film (Kodak 649) was exposedfor 30 seconds to a step-wedge and fixed to remove all non-photolyzedsilver halide. The invisible latent image was then amplified byimmersion in a mixture comprising ml. of 1 M aqueous ascorbic acid, 50ml. of 1 M aqueous Cu(NO and 50 ml. of 0.75 M triethanol amine in 50:50H O-methanol. After seconds, 15 steps were visible. The maximum opticaldensity was about 1.33.

EXAMPLE 19 The paper copy medium of Examples 1-17, coated with titaniumdioxide in an acrylate resin binder, was soaked for 5 minutes in a 5%aqueous solution of cupric nitrate, and then dried. The dry paper wasexposed to a 6 watt black light Raymaster fluorescent bulb for 60seconds, then immersed for 150 seconds in a mixture comprising 10 ml. of1 M aqueous ascorbic acid, 10 ml. of l M aqueous Cu(NO and 10 ml. of0.75 M triethanol amine in 50:50 H O--CH OH. A black image having anoptical density of 0.92 resulted.

In an alternative method, the paper can first be exposed and thencontacted with a cupric ion solution. n heating to about 75 C., thecuprous ion formed by reaction of the cupric ion and activated TiOdisproportionates to cupric ion and copper. The latent copper image canbe amplified with the solution disclosed herein.

EXAMPLE 20 Paper treated with cupric nitrate as in Example 19 wasexposed after drying, and was then immersed for amplification in amixture comprising ml. of 1 M aqueous ascorbic acid and 1-0 ml. of 0.75M triethanol amine solution for a period of 180 seconds. A bluish-blackimage having an optical density of 0.95 was produced. In this case, thecupric ion reacting was ascorbic acid for image intensification of thelatent copper image was supplied by the residual copper ion in thecoating.

EXAMPLE 21 A primary silver image prepared as in Examples 1-17 wasimmersed for amplification in a solution comprising 25% water and 75%methanol. The concentration of Cu(N0 in said aqueous-methanol solutionwas 0.25 M and the concentration of ascorbic acid in said solution wasalso 0.25 M. After immersion for about 180 seconds, a purple image wasobtained which had an optical density of about 1.01.

In formulating image intensification solutions comprising cupric ion andascorbic acid in combination with an acid acceptor, the cupric ion andascorbic acid are preferable first combined and the acid acceptor addedsubsequently since if the acid acceptor is added directly to the cupricion, precipitation of copper hydroxides may result. Apparently, ifascorbic acid is added first to the copper ion, complexes may be formedbetween the acid and copper ion which tend to discourage formation ofcopper hydroxides.

Prints produced by the present process are suitably dried soon aftertheir production to discourage air oxidation of, deposited copper in thepresence of moisture.

The copper salts used to supply cupric ion are not critical, nor are thesolvents employed in preparing the compositions of the invention. Thesolvents should not cause formation of copper hydroxides, and should bemiscible with the acid acceptor desired. In general, aqueous solutions,or solutions in lower alcohols are employed, as are mixtures of waterand a lower alcohol such as methanol.

The chemical deposition of copper for amplification of images in a copymedium according to the present invention must be distinguished fromprior art processes using the electrical deposition or electroplating ofcopper to render metal latent images visible. No passage of electriccurrent is required or used in the present invention, and the copy mediaemployed are not limited to those having conductive carriers to whichelectrical contact can be made. Insulating carriers such as of ordinarypaper, glass, or cloth or wood are acceptable in the present invention.

Although specific embodiments have been shown and described herein, itwill be understood that they are illustrative and are not to beconstrued as limiting on the scope and spirit of the invention.

What is claimed is:

1. The method of amplifying a metallic image of a metal at least asnoble as copper, which method comprises contacting a physicallydevelopable copy medium comprising said metallic image with ascorbicacid and cupric ion to deposit selectively metallic copper in imageareas of said copy medium where metal is already present.

2. The method as in claim 1 wherein a nitrogenous acid acceptor isadditionally present with said ascorbic acid and said cupric ion.

3. The method as in claim 1 wherein said metallic image comprises metalselected from the group consisting of copper and silver.

4. The method of amplifying a latent metallic image in a copy mediumwhich comprises contacting a copy medium comprising a latent metallicimage with a developer comprising ascorbic acid and cupric ion todepositselectively metallic copper in areas containing the latent image.

5. A process as in claim 4 wherein the latent metallic image is producedby exposing a photosensitive medium comprising a photoconductor andcontacting said medium with image-forming materials comprising asolution of metal ions of a metal at least as noble as copper.

6. A process as in claim 4 wherein the latent metallic image is producedby exposing a copy medium comprising photosensitive silver halide.

7. The method as in claim 4 wherein said latent metallic image comprisesa metal at least as noble as copper.

8. The method as in claim 7 wherein said medium is contacted with cupricion ascorbic acid and an acid acceptor which acid acceptor does notprecipitate copper hydroxides.

9. The method as in claim 7 wherein a copy medium having cupric ionthereon is contacted with a solution of ascorbic acid and of an acidacceptor which acid acceptor does not precipitate copper hydroxides.

10. The method as in claim 7 wherein said latent metallic imagecomprises metallic silver.

11. The method as in claim 7 wherein said latent metallic imagecomprises metallic copper.

12. In the method of image reproduction which comprises exposing a copymedium to activating radiation, said copy medium comprising aphotosensitive material rendered capable, by exposure to said radiation,of reducing silver ion to metallic silver on contact, and contactingsaid exposed medium to silver ion prior to, at the time of, orsubsequent to the exposure step to form a latent image of metallicsilver in said copy medium, the improvement wherein said latent silverimage is amplified and made visible by contact of said medium withascorbic acid and cupric ion.

13. The method of producing a visible image in a copy medium comprisingtitanium dioxide and cupric ion, which method comprises exposing saidmedium to form a latent image of metallic copper in said copy medium,and then amplifying and making said latent image visible by contactingsaid medium with ascorbic acid and cupric 14. A developed copy mediumhaving a visible image therein, said medium comprising a carrier and animage formed therein by a first metallic latent silver image and asecond, heavier, visible overlying metallic copper image.

15. A copy medium as in claim 14 wherein said carrier is electricallyinsulating.

16. A developed .photosenitive copy medium comprising a carrier and avisible image comprising a first latent image of a metal more noble thanmetallic copper and a second, heavier, visible overlying metallic copperimage.

17. A copy medium as in claim 16 wherein the carrier is electricallyconductive.

18. A copy medium as in claim 16 wherein the copy medium comprises atleast one member selected from the group consisting of silver halide anda photoconductor.

19. A copy medium as in claim 16 wherein the copy medium comprises aphotosensitive titanium dioxide.

20. A composition for the amplification of images formed in a copymedium by the presence therein of a 7 8 metal, which compositioncomprises a solution of cupric OTHER REFERENCES an acid acceptor andascorbic acid in a common Chemical Abstract 52: 16020 of Netadas et a1.Compt. solvent and wherein the acid acceptor is at least one mem- Rend246 2543 5 (1958) ber of the group consisting of ammonium hydroxide andNeijgrgan et aL'General Chemistry 1959 an Organic amine. 5

References Cited UNITED STATES PATENTS NORMAN G. TORCHIN, PrimaryExaminer M. F. KELLEY, Assistant Examiner 2,854,386 9/1958 Lyman et a1.9660 3,152,903 10/1964 Shepard et a1. 9664 10 US Cl XR FOREIGN PATENTS9660 637,058 5/1964 Belgium.

